Investments - Gross Unrealized Losses for Fixed Maturities (Details) $ in Millions	Jun. 30, 2023 USD ($) item	Dec. 31, 2022 USD ($) item
Gross Unrealized Losses for Fixed Maturities
Fixed maturities, Less than twelve months, Fair value	$ 15,376.8	$ 45,651.0
Fixed maturities, Less than twelve months, Gross unrealized losses	607.7	6,183.1
Fixed maturities, Greater than or equal to twelve months, Fair value	39,099.0	8,850.9
Fixed maturities, Greater than or equal to twelve months, Gross unrealized losses	6,572.4	1,695.2
Fixed maturities, Total, Fair value	54,475.8	54,501.9
Fixed maturities, Total, Gross unrealized losses	7,180.1	7,878.3
U.S. government and agencies
Gross Unrealized Losses for Fixed Maturities
Fixed maturities, Less than twelve months, Fair value	543.7	1,528.3
Fixed maturities, Less than twelve months, Gross unrealized losses	15.5	209.4
Fixed maturities, Greater than or equal to twelve months, Fair value	938.3	181.5
Fixed maturities, Greater than or equal to twelve months, Gross unrealized losses	221.6	41.8
Fixed maturities, Total, Fair value	1,482.0	1,709.8
Fixed maturities, Total, Gross unrealized losses	237.1	251.2
Non-U.S. governments
Gross Unrealized Losses for Fixed Maturities
Fixed maturities, Less than twelve months, Fair value	116.3	407.5
Fixed maturities, Less than twelve months, Gross unrealized losses	4.6	57.7
Fixed maturities, Greater than or equal to twelve months, Fair value	283.1	19.9
Fixed maturities, Greater than or equal to twelve months, Gross unrealized losses	53.4	7.1
Fixed maturities, Total, Fair value	399.4	427.4
Fixed maturities, Total, Gross unrealized losses	58.0	64.8
States and political subdivisions
Gross Unrealized Losses for Fixed Maturities
Fixed maturities, Less than twelve months, Fair value	1,162.2	5,303.5
Fixed maturities, Less than twelve months, Gross unrealized losses	54.3	1,008.9
Fixed maturities, Greater than or equal to twelve months, Fair value	4,711.8	391.9
Fixed maturities, Greater than or equal to twelve months, Gross unrealized losses	986.5	127.8
Fixed maturities, Total, Fair value	5,874.0	5,695.4
Fixed maturities, Total, Gross unrealized losses	1,040.8	1,136.7
Corporate debt securities
Gross Unrealized Losses for Fixed Maturities
Fixed maturities, Less than twelve months, Fair value	7,996.1	27,309.5
Fixed maturities, Less than twelve months, Gross unrealized losses	387.8	3,944.6
Fixed maturities, Greater than or equal to twelve months, Fair value	21,038.8	2,944.1
Fixed maturities, Greater than or equal to twelve months, Gross unrealized losses	3,726.2	698.0
Fixed maturities, Total, Fair value	29,034.9	30,253.6
Fixed maturities, Total, Gross unrealized losses	4,114.0	4,642.6
Residential mortgage-backed pass-through securities
Gross Unrealized Losses for Fixed Maturities
Fixed maturities, Less than twelve months, Fair value	1,159.3	1,201.7
Fixed maturities, Less than twelve months, Gross unrealized losses	24.7	97.5
Fixed maturities, Greater than or equal to twelve months, Fair value	1,151.5	574.8
Fixed maturities, Greater than or equal to twelve months, Gross unrealized losses	168.2	105.7
Fixed maturities, Total, Fair value	2,310.8	1,776.5
Fixed maturities, Total, Gross unrealized losses	192.9	203.2
Commercial mortgage-backed securities
Gross Unrealized Losses for Fixed Maturities
Fixed maturities, Less than twelve months, Fair value	399.7	3,648.5
Fixed maturities, Less than twelve months, Gross unrealized losses	12.6	484.0
Fixed maturities, Greater than or equal to twelve months, Fair value	4,242.4	1,124.8
Fixed maturities, Greater than or equal to twelve months, Gross unrealized losses	699.6	222.5
Fixed maturities, Total, Fair value	4,642.1	4,773.3
Fixed maturities, Total, Gross unrealized losses	712.2	706.5
Collateralized debt obligations
Gross Unrealized Losses for Fixed Maturities
Fixed maturities, Less than twelve months, Fair value	899.0	2,832.2
Fixed maturities, Less than twelve months, Gross unrealized losses	9.5	89.0
Fixed maturities, Greater than or equal to twelve months, Fair value	2,947.0	1,330.1
Fixed maturities, Greater than or equal to twelve months, Gross unrealized losses	93.3	54.7
Fixed maturities, Total, Fair value	3,846.0	4,162.3
Fixed maturities, Total, Gross unrealized losses	102.8	143.7
Other debt obligations
Gross Unrealized Losses for Fixed Maturities
Fixed maturities, Less than twelve months, Fair value	3,100.5	3,419.8
Fixed maturities, Less than twelve months, Gross unrealized losses	98.7	292.0
Fixed maturities, Greater than or equal to twelve months, Fair value	3,786.1	2,283.8
Fixed maturities, Greater than or equal to twelve months, Gross unrealized losses	623.6	437.6
Fixed maturities, Total, Fair value	6,886.6	5,703.6
Fixed maturities, Total, Gross unrealized losses	722.3	729.6
Principal Life Insurance Company
Gross Unrealized Losses for Fixed Maturities
Fixed maturities, Less than twelve months, Fair value	14,341.6	44,857.0
Fixed maturities, Less than twelve months, Gross unrealized losses	543.7	6,096.3
Fixed maturities, Greater than or equal to twelve months, Fair value	38,367.1	8,496.1
Fixed maturities, Greater than or equal to twelve months, Gross unrealized losses	6,467.1	1,645.1
Fixed maturities, Total, Fair value	52,708.7	53,353.1
Fixed maturities, Total, Gross unrealized losses	$ 7,010.8	$ 7,741.4
Available-for-sale Securities, Continuous Unrealized Loss Position, Qualitative Disclosure
Available-for-sale Securities in Unrealized Loss Positions, Qualitative Disclosure, Percent Investment Grade (as a percent)	94.00%	94.00%
Available-for-sale Securities in Unrealized Loss Positions, Qualitative Disclosure, Average Price (percent of carrying value to amortized cost)	88.00%	87.00%
Available-for-sale Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions, Less Than Twelve Months \| item	2,981	7,589
Available-for-sale Securities in Unrealized Loss Positions, Average Price, Less Than Twelve Months (percent of carrying value to amortized cost)	96.00%	88.00%
Available-for-sale Securities in Unrealized Loss Positions, Percent Investment Grade, Less Than Twelve Months (as a percent)	92.00%	95.00%
Available-for-sale Securities in Unrealized Loss Position, Aggregate Losses On Investment Grade Investments, Less Than Twelve Months	$ 517.9	$ 5,920.4
Available-for-sale Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions, Twelve Months or Longer \| item	6,610	1,654
Available-for-sale Securities in Unrealized Loss Positions, Average Price, Twelve Months or Longer (percent of carrying value to amortized cost)	86.00%	84.00%
Principal Life Insurance Company \| States and political subdivisions
Gross Unrealized Losses for Fixed Maturities
Fixed maturities, Greater than or equal to twelve months, Gross unrealized losses	$ 978.3	$ 126.8
Available-for-sale Securities, Continuous Unrealized Loss Position, Qualitative Disclosure
Available-for-sale Securities in Unrealized Loss Positions, Average Price, Twelve Months or Longer (percent of carrying value to amortized cost)	83.00%	75.00%
Principal Life Insurance Company \| Corporate debt securities
Gross Unrealized Losses for Fixed Maturities
Fixed maturities, Greater than or equal to twelve months, Gross unrealized losses	$ 3,633.5	$ 654.9
Available-for-sale Securities, Continuous Unrealized Loss Position, Qualitative Disclosure
Available-for-sale Securities in Unrealized Loss Positions, Average Price, Twelve Months or Longer (percent of carrying value to amortized cost)	85.00%	80.00%
Principal Life Insurance Company \| Commercial mortgage-backed securities
Gross Unrealized Losses for Fixed Maturities
Fixed maturities, Greater than or equal to twelve months, Gross unrealized losses	$ 694.5	$ 220.9
Available-for-sale Securities, Continuous Unrealized Loss Position, Qualitative Disclosure
Available-for-sale Securities in Unrealized Loss Positions, Average Price, Twelve Months or Longer (percent of carrying value to amortized cost)	86.00%	83.00%
Principal Life Insurance Company \| Collateralized mortgage obligation security
Gross Unrealized Losses for Fixed Maturities
Fixed maturities, Greater than or equal to twelve months, Gross unrealized losses	$ 508.1	$ 320.2
Available-for-sale Securities, Continuous Unrealized Loss Position, Qualitative Disclosure
Available-for-sale Securities in Unrealized Loss Positions, Average Price, Twelve Months or Longer (percent of carrying value to amortized cost)	83.00%	81.00%

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Amount of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), in continuous unrealized loss position for more than 12 months, without allowance for credit loss. Includes beneficial interest in securitized financial asset.

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